| In this thesis,a theoretical study was carried on the reaction of N-X and C-X bonds formation catalyzed/activated by transition metal complexes.The following contents are included:the first part is N-N activation by dinuclear dinitrogen transition-metal complexes,the second part is cobalt catalyzed Suzuki-Miyaura cross coupling,and the third part is C-N bond construction and C=O double bond cleavage catalyzed by titanium oxonitride.1.N-N activation by dinuclear dinitrogen transition-metal complexes studied 90 kinds of dinitrogen binuclear transition-metal complexes at singlet and triplet states in Group 4-10 from Period 4 to 6 based on the biomimetic dinitrogen fixation species using density functional theory(DFT)method,[Cp*Fe(?-?2:?2-bdt)(?-?1:?1-MeN=NMe)FeCp*]and[Cp*Fe(?-SEt)2(?-?1:?1-MeN=NMe)FeCp*],in order to investigate the transtion-metal effect in N-N activation using DFT method.The calculated results indicate that N-N bond activation is strongly related to the period of transition metal.N-N activation by transition metals in Period 6 is stronger than those in Period 5 and Period 4.For transition metals in the same period,N-N activation ability decreases from Group 4 to Group 10.The odd-even electron number of transition metal center also shows certain influence on the N-N activation.In addition,side-on coordination mode is more favorable than end-on mode for thiolate-bridged dinuclear transiton-metal complexes on N-N bond activation.The type of ligands(BDT ligand or ethyl ligand)in this system has little impact on N-N activation.2.The reaction mechanism of cobalt catalyzed Suzuki-Miyaura cross coupling was studied at b31yp level using DFT method.The bidentate ligand iPrPNP will dissociate one of the phosphine ligand from the metal center in the reaction so that the metal center to get more space steric.In the first step,hydrogen transfer from the intermediate 1-2 directly to generate the cobalt(I)alkoxides(iPrPNP)CoOR is more advantageous and the hydrogen transfer is the the rate-determining step with the free energy barrier of 7.9 kcal/mol.The cobalt(I)alkoxides(iPrPNP)CoOR jump to triplet from singlet before the process of transmetalation as the second step,process for coordination of O-B generate the intermediate 2r2 with sp3 hybrid tetrahedron configuration is the rate-determining step with the free energy barrier of 23.4 kcal/mol.In the first two steps of the catalytic cycle,the metal center cobalt keeps Co(I).Inaddition,cobalt(?)complexes has shown high(triplet)and low(singlet)spin state.And we also speculate on the path of the process for third-step the product formation.After the theoretical calculations for five substituents and benzene-substituted cobalt complexes in the alkoxides formation step we found that the influence of different substituents toward the reaction rate.The volume of the substituents leads to differences in steric hindrance,which in turn affects the reaction rate and the progress of the reaction.3.The reaction mechanism of titanium oxonitride catalyzed C-N bond construction and C=O double bond cleavage and the substitution modulation effect of ketones(R2C=O)were studied in density functional theory.There are two different reaction modes in the addition reaction:(A)The C=O bond in 2 is cleaved to form intermediate 5,and then the product 3 is generated through the transition state TS35.(B)The substrate is first added to complex 1,O at complex 2 coordinated with Ti2 to generate the intermediate 4 with the oxygen bridge bond,the C=O bond breaks to generate 3.The theoretical calculations results indicates that Path A is more favourable.We clarify the mechanism of C-N bond activation using the front molecular orbital(FMO)and natural bond orbital(NBO)method.We also studied the substituent effect(R=H,Me,Et,tBu,Ph,F,Cl)in the substrate to research C=O bond cleavage and C-N bond formation,and the results show that in the reaction process of different alkyl and aryl substituents,the effect of space steric hindrance effect is stronger than its electronic effect. |
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